[LAD] Audio Trigger

Patrick Shirkey pshirkey at boosthardware.com
Thu Nov 6 10:49:53 UTC 2008

OrazioPirataDelloSpazio (Lorenzo) wrote:
> Hi all,
> I need to use a microphone input as a trigger. In other words my idea is 
> to connect a switch to the microphone input. In this way, when the 
> switch is turned on it generates a spike in the captured track.
> I would like to create a program that trigger an event every spike it 
> receives.
> I succeed in capturing the mic input through a simple program that uses 
> alsa driver, but I don't know how to "parse" the raw data to search for 
> the spikes. Any hints?
There are a couple of gates in the ladspa/swh/etc... kits. This is 
generally what they are used for.

> Second question: on a "full duplex" sound card, can I capture at 8 bit, 
> mono, 22.050 bit/s , and on the same time playback at 16 bit, stereo, 
> 44.100 ?
It depends on the cards capabilities. Some consumer cards can only 
manage playback at 48000hz.

You can find out with

cat /proc/asound/card0/codec

look for the AudioOutput and AudioInput to see what the card can do. 
There may be more details in other nodes depending on your card.

> Thank you!
> Lorenzo
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Patrick Shirkey
Boost Hardware Ltd.

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